It probably depends on what you are planning on growing at the plot. My understanding is that if you are growing melons or other sun lovers, 3 hours of sun will make a difference since they like a full day of sun. If you are growing tomatoes and peppers, I have grown them in a cooler zone with 6 hours of direct sun and they did just fine.

Another thing to think about is whether disease pressure is high where you are. Where I am we have humid summer that leads to fungal disease like early and late blight. The sooner I can have direct sun to dry off the leaves in the morning, the better off I am. Since you are in CA, you may just have dry summers then this wouldn't be a problem for you.

I grow huge tomato plants in only 4.5 hours of sunlight. So sun is probably not the issue. Perhaps it's the soil and/or fertilizer?

I'd say it is much more # 1 and especially #2 rather than the sun.

#1 you really can't compare the growth of Early Girls to yours unless your's are early varieties too.

#2 compost is primarily a soil amendment not a fertilizer. The nutrients in it aren't available to the plants unless you have sufficient soil bacteria to convert it and then not until after the soil bacteria convert them to a useable form. So while it will benefit your plants next year it can't do much for them now.

I use loads of compost 2x a year in my garden but it is the compost added last year and the year before and the millions of beneficial soil bacteria that have developed in it that is feeding my plants, not what I just added.

So your plants need to be fed. Something well balanced across the board with N-P-K and micro-nutrients. If you don't want to use synthetic fertilizers, fine. There are any number of organic fertilizers available that your plants will be able to benefit from immediately.

Dave

In addition to direct sunlight, factor in ambient light. Last year tomatoes grown in great soil with about 4 hours direct sun, but rest of the day plenty of ambient light, did much better than row of tomatoes growing in so-so soil in full sun all day. This year that so-so row are in their 2nd year and going gangbusters. Last year's top performers were replaced by sweet peas, so no way to compare the two on a 2nd year. But a tomatoe that I planted nearby, just because I couldn't bear to throw it away...under an avocado and in back of a kumquat .... is growing like crazy and setting fruit better than it's better-situated 6-pack buddies. The point is, that breaking the 'rules' is worth a try, if that is your only choice. And besides, no guarantees, even when you follow all the rules.

My toms have plenty of light but didn't take off until I started a regular fertilizing program. Now they grow rather fast and tall. More knowledge for next year.

Thanks everyone. I'm doing at at-home soil test right now. I have a raised bed and added about 10 inches of new soil to the garden because it was low. I have a feeling it was nutrient-less.

The year isn't over yet - we have a mild climate (bay area of CA) and can grow well into september at least. I'll likely be fertilizing tomorrow.

Thanks everyone!

You need fertilizer. Too many newbie gardeners think compost is fertilizer...it is not. There is an old gardening cliche..."if you want your garden to feed you, you have to feed your garden".

FWIW, I was told that if you have a choice between morning sun and afternoon sun, that morning sun is better for plants. The person who told me is a gardener who specializes in small urban gardens where sunlight is often an issue. She said that plants respond better to morning sun. I don't know if this is so, but it is something to think about. If you can have a plot with morning sun, you might get more out of it.

I don't have any place in my (small urban) yard where I get sun all day. I think I do pay a price in production because of this. All other things being equal, I suspect I would probably get more fruit if I had more sun. But I can't move my neighbors' houses, so I manage with what I have.

One thing to consider: if that has been a community garden for awhile and you have just started with that plot, the soil might have not been properly cared for before you received the use of the plot.

It might take you a couple of years to get the soil into top condition. If you keep the same plot year after year, I suggest that you feed your plants now and then in the fall turn a couple of loads of manure into the soil.

Mulch your plants with anything you can find that will end up as a good soil amendment. Think about planting a green manure crop over the winter. Your neighbors might go in on that with you, especially if the entire community garden gets tilled in the spring.

Turn more compost under in the spring before you plant.

After that, you can just keep mulching with organic matter and the soil will get better and better.

If you are trying to grow organic, there are lot of organic fertilizers that you can use to feed your crops.